Beware of Dog
The dog may be man's best friend, but he's not always a good friend to man's air conditioning equipment. Dogs love to chew and it's not unusual for dogs to bite through the wire running to an outdoor condenser unit. Some dogs actually get a buzz from the mild shock and will repeat the behavior.
Each year ACU Air gets calls from customers whose air conditioners have quit working after their dogs have chewed through the wiring to their outside condenser units. We have also seen cases in which condensers located in yards with few or no trees have served as surrogate fire hydrants for male dogs. Over time, the acid from the dogs' urine has deteriorated the condenser unit's casing and coil to the point that the entire unit has to be replaced. If you have a dog that likes to chew or that lifts his leg on your condenser, consider fencing off the unit. Make sure that there is a gate wide enough to allow for the removal of the unit should it ever need to be replaced.
If you don't have floor vents, you will not have to wory about this last issue. If you do have floor vents and a single pet occassionally lies down on a single vent, it should not create a serious problem -- but take care not to allow multiple pets to restrict the flow of air from multiple vents. This could overtax your heating and cooling system, not to mention run up your utility bills!